Also known as Accuracy, Bias is an estimate of the error in the measurement system. Bias is estimated by taking repeat samples of a part or standard using the measurement system, and comparing the average of these measurements with a measurement taken of the same piece using equipment with higher accuracy.
BIAS = Average of Measurements – Reference Value
% Bias = (Bias / Process Variation) * 100%
PV is the Process Variation, which may be estimated as 6 times the Process Sigma value calculated from a control chart.